Many food and beverage products contain nutritive sweeteners such as sucrose (generally referred to as ‘sugar’ or ‘table sugar’), glucose, fructose, corn syrup, high fructose corn syrup and the like. Such sweeteners supply not only sweetness to the food and beverage products, but also bulk, texture and desirable functional properties such as browning, humectancy, freezing point depression and the like. They also produce a favorable sensory response, for example in terms of quality of sweetness, lack of bitterness and off taste, desirable temporal profile and desirable mouthfeel.
Although desirable in terms of taste and functional properties, excess intake of nutritive sweeteners, such as sucrose, has long been associated with an increase in diet-related health issues, such as obesity, heart disease, metabolic disorders and dental problems. This worrying trend has caused consumers to become increasingly aware of the importance of adopting a healthier lifestyle and reducing the level of nutritive sweeteners in their diet.
In recent years, there has been a movement towards the development of replacements for nutritive sweeteners, with a particular focus on the development of low or zero-calorie sweeteners. An ideal replacement for a nutritive sweetener is a sweetener that has the same desirable taste characteristics and functional properties as the nutritive sweetener, but which also has fewer calories. Aiming to meet this growing need, the market has been flooded with possible candidates to replace conventional nutritive sweeteners. Unfortunately, however, many of the low or zero calorie replacements offered on the market lack one or all of the necessary characteristics, and often exhibit bitterness or off-taste. Therefore, many of the proposed sweeteners are not an ideal replacement for nutritive sweeteners.
One proposed alternative to nutritive sweeteners is allulose (also known as D-psicose). Allulose is known as a “rare sugar”, since it occurs in nature in only very small amounts. It provides around 70% of the sweetness of sucrose, but only around 5% of the calories (approximately 0.2 kcal/g). It may therefore essentially be considered to be a ‘zero calorie’ sweetener.
In view of its scarcity in nature, production of allulose relies on the epimerization of readily available fructose. Ketose-3-epimerases can interconvert fructose and allulose, and various ketose-3-epimerases are known for carrying out this conversion.
U.S. Pat. No. 8,030,035 and PCT Publication No. WO2011/040708 disclose that D-psicose (an alternative name for allulose) can be produced by reacting D-fructose with a protein derived from Agrobacterium tumefaciens, and having psicose 3-epimerase activity.
US Patent Publication No. 2011/0275138 discloses a ketose 3-epimerase derived from a microorganism of the Rhizobium genus. This protein shows a high specificity to D- or L-ketopentose and D- or L-ketohexose, and especially to D-fructose and D-psicose. This document also discloses a process for producing ketoses by using the protein.
Korean Patent No. 100832339 discloses a Sinorhizobium YB-58 strain which is capable of converting fructose into psicose (i.e. allulose), and a method of producing psicose using a fungus body of the Sinorhizobium YB-58 strain.
Korean Patent Application No. 1020090098938 discloses a method of producing psicose using E. coli wherein the E. coli expresses a polynucleotide encoding a psicose 3-epimerase.
Allulose is present in processed cane and beet molasses, steam-treated coffee, wheat plant products and high fructose corn syrup. D-allulose is the C-3 epimer of D-fructose and the structural differences between allulose and fructose result in allulose not being metabolized by the human body to any significant extent, and thus having “zero” calories. Thus, allulose is thought to be a promising candidate as a replacement for nutritive sweeteners and as a sweet bulking agent, as it has no calories and is reported to be sweet while maintaining similar properties to sucrose. However, the use of allulose alone as a replacement for nutritive sweeteners may have some limitations due to cost and digestive tolerance in some applications.
Alternative sweeteners on the market include sucralose and fructose. Sucralose is a ‘high potency’ or ‘high intensity’ sweetener that is approximately 600 times as sweet as sucrose. Fructose (also known as “fruit sugar”) is a 6-carbon polyhydroxyketone monosaccharide sugar that is often found in plants and in honey. The monosaccharide is found in crystalline form, often referred to as D-fructose. Fructose can also be found as a component of other sweeteners such as high-fructose corn syrup (HFCS), which is a mixture of glucose and fructose. Fructose is frequently used to enhance the sweetness and taste of food and beverage products. Using fructose as a replacement for sucrose and other nutritive sweeteners also has its limitations, as fructose is fully caloric and thus does not provide an effective calorie reduction strategy.
Therefore, there is a need to provide an improved replacement for nutritive sweeteners that has low calories and is without limitations in use, but which also has taste characteristics and functional properties similar to those of sucrose and other nutritive sweeteners.